Acute forces required for fatal compression asphyxia: A biomechanical model and historical comparisons

Prone restraint cardiac arrest in in-custody and arrest-related deaths

We postulate that most atraumatic deaths during police restraint of subjects in the prone position are due to prone restraint cardiac arrest (PRCA), rather than from restraint asphyxia or a stress-induced cardiac condition, such as excited delirium. The prone position restricts ventilation and diminishes pulmonary perfusion. In the setting of a police encounter, metabolic demand will be high from anxiety, stress, excitement, physical struggle, and/or stimulant drugs, leading to metabolic acidosis and requiring significant hyperventilation. Although oxygen levels may be maintained, prolonged restraint in the prone position may result in an inability to adequately blow off CO₂ , causing blood pCO₂ levels to rise rapidly. The uncompensated metabolic acidosis (low pH) will eventually result in loss of myocyte contractility. The initial electrocardiogram rhythm will generally be either pulseless electrical activity (PEA) or asystole, indicating a noncardiac etiology, more consistent with PRCA and inconsistent with a primary role of any underlying cardiac pathology or stress-induced cardiac etiology. We point to two animal models: in one model rats unable to breathe deeply due to an external restraint die when their metabolic demand is increased, and in the other model, pressure on the chest of rats results in decreased venous return and cardiac arrest rather than death from asphyxia. We present two cases of subjects restrained in the prone position who went into cardiac arrest and had low pHs and initial PEA cardiac rhythms. Our cases demonstrate the danger of prone restraint and serve as examples of PRCA.

Prone restraint cardiac arrest: A comprehensive review of the scientific literature and an explanation of the physiology

Deaths occurring among agitated or violent individuals subjected to physical restraint have been attributed to positional asphyxia. Restraint in the prone position has been shown to alter respiratory and cardiac physiology, although this is thought not to be to the degree that would cause asphyxia in a healthy, adult individual. This comprehensive review identifies and summarizes the current scientific literature on prone position and restraint, including experiments that assess physiology on individuals restrained in a prone position. Some of these experimental approaches have attempted to replicate situations in which prone restraint would be used. Overall, most findings revealed that individuals subjected to physical prone restraint experienced a decrease in ventilation and/or cardiac output (CO) in prone restraint. Metabolic acidosis is noted with increased physical activity, in restraint-associated cardiac arrest and simulated encounters. A decrease in ventilation and CO can significantly worsen acidosis and hemodynamics. Given these findings, deaths associated with prone physical restraint are not the direct result of asphyxia but are due to cardiac arrest secondary to metabolic acidosis compounded by inadequate ventilation and reduced CO. As such, the cause of death in these circumstances would be more aptly referred to as "prone restraint cardiac arrest" as opposed to "restraint asphyxia" or "positional asphyxia."

Restraint physiology: A review of the literature

Law-enforcement often uses forensic restraints to control individuals and often these individuals are placed in positions and with various amounts of weight used to hold them in place. There has been a moderate amount of research performed on humans in this field of study to assess the physiologic impact of the positions and weight on ventilatory and cardiovascular parameters. This review discusses the scientific medical literature on the use of restraints and restraint position including the use of weight force and aggregates the findings in specific physiologic areas, such as impact on blood pressure, heart rate, and ventilatory parameters.

Experimental study on individual risk in crowds based on exerted force and human perceptions

Frequent and intense interactions between individuals inevitably occur in crowd disasters. Previous studies indicate that the primary risk evaluation parameters for individuals in crowds during these interactions are exerted force and its duration. In this study, a series of controlled laboratory experiments simulating static and fluctuant loads were conducted to obtain real-time exerted force data and the associated individual subjective feelings. An individual risk evaluation method is then established to assign a specific individual risk value to each data set of exerted force and its duration according to the individuals' feelings. This method divides the range of risk value into three zones: comfortable zone, uncomfortable zone and crisis zone. The transition from an uncomfortable zone to crisis zone is not a single numerical value but a range that considers individual differences. The method presented in this paper can assist in developing pedestrian simulation models as well as managing crowd events. Practitioner summary: Accident surveys indicate that casualties and injuries usually occur under a long-term static load or heavy dynamic load. We tested human body extrusion experiments in four conditions, measured the real-time load intensity and duration of the individual's action on the thoracic cavity during the mutual extrusion process, and an individual risk evaluation method has been established based on the force exerted on the body and its duration to prevent crowd disasters. Abbreviations: NIST: National Institute of Standards and Technology; IREM: individual risk evaluation method; CPR: cardiopulmonary resuscitation.